Statements Of Cash Flows (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Operating activities
Net income	$ 213,749	$ 123,778
Adjustments to reconcile net income to net cash provided by operating activities:
Net amortization of premium related to mortgage-backed securities	60,719	30,213
Amortization related to interest rate swap agreements	253	168
Share based compensation expense	735	1,153
Hedge ineffectiveness	516	300
Gain on sale of mortgage-backed securities	(17,735)	(7,767)
Changes in operating assets and liabilities:
(Increase) decrease in accrued interest receivable	(25,900)	1,743
Increase in other assets	(1,199)	(490)
Decrease in accrued interest payable	(849)	(475)
Increase (decrease) in accounts payable and other liabilities	165	(483)
Net cash provided by operating activities	230,454	148,140
Investing activities
Purchases of mortgage-backed securities	(11,327,766)	(2,812,829)
Principal repayments of mortgage-backed securities	2,360,742	1,889,571
Sale of mortgage-backed securities	1,037,064	331,857
Net cash used in investing activities	(7,929,960)	(591,401)
Financing activities
Issuance of common stock, net of cost of issuance	853,441	271,377
Cash dividends paid	(179,280)	(128,333)
Increase in restricted cash	(204,114)	(62,053)
Proceeds from repurchase agreements	118,620,023	54,686,260
Principal repayments on repurchase agreements	(111,414,852)	(54,354,352)
Net cash provided by financing activities	7,675,218	412,899
Net decrease in cash and cash equivalents	(24,288)	(30,362)
Cash and cash equivalents, beginning of period	112,626	225,828
Cash and cash equivalents, end of period	88,338	195,466
Supplemental disclosure of cash flow information
Cash paid during the period for interest	103,211	71,658
Supplemental schedule of non-cash financing activities
Obligation to brokers incurred for purchase of mortgage-backed securities	$ 1,395,612	$ 1,961,415